The starting materials for the novel synthesis of prostaglandin intermediates disclosed herein are iridoid glycosides. These are a group of naturally occurring compounds characterized by the cyclopentanopyran ring system shown and numbered below ##STR1##
In all of the compounds, a .beta. glucosyloxy group (indicated as glu) is present on C-1 and a double bond between C-3 and C-4, giving rise to the characteristic enol ether. C-10 and C-11 may or may not be present. In the plumieride series four additional carbons are present attached to C-10. The compounds are further characterized by the presence of several oxygen functions in the aglucone. These may be hydroxyl groups, alkoxyl groups, acyloxy groups or epoxides. A double bond is frequently present in the cyclopentane ring. These various combinations have given rise to about 27 known glucosides and some 15 related nonglucosidic substances.
The 10 carbon aglucones are of particular interest in the present invention. These include asperuloside, deacetylasperuloside, paederoside (these all have the closed 5 membered ring between C-4 and C-6 on the basic iridoid system. Scandoside, daphylloside and paederosidic acid lack ring closure. The ring may be closed subsequently.
The structures are shown below. ##STR2##
Isolation is generally affected by (a) adsorption and elution from charcoal, (b) the use of lead acetate as a clarifying agent and (c) direct Soxhlet extraction with an organic solvent. The plant extracts are available from Hines Wholesale Nurseries, Santa Ana, Calif. and Strybing Arboretum, San Francisco, Calif.